Most of the middle repetitive DNA in Drosophila melanogaster, roughly one sixth of the genome, is composed of families of 10-100 repeated elements that are found at scattered locations in the chromosome arms and occupy new chromosomal positions as populations of D. melanogaster diverge (Young, Proc, Natl. Acad. Sci. 76:6274). We will be asking the following questions about these sequences: 1) How much of the genome is affected by the reshuffling of repeated DNA? 2) What is the relationship of extrachromosomal, middle repetitive DNA to chromosomal dispersed repeated DNA? 3)Can we observe gene movement? 4) What is the consequence of deleting a repeated gene family? 5) Is the syndrome of hybrid dysgenesis in D. melanogaster dependent on transposable elements? 6) Will a repeated sequence from Drosophila be mobilized in yeast? 7) Can dispersed, repeated DNA provide a system for identifying changes in the structure of unique sequence DNA that occur during development? We will also initiate a study of the Notch locus of D. melanogaster and are interested in the following problems: 1) How big is this gene? 2) How many gene products are specified by the Notch locus?